Aerogel

Background

The heating requirement in Germany amounts to more than half of the total energy consumption. Approx. 50% is used to heat rooms, followed by process heat and hot water. The share of renewable energies in heating demand was around 10% in 2016. With two thirds, biomass provides the largest share of renewable energy sources, with solar thermal power accounting for 5.2 % 1. MIT has developed a substance that enables solar thermal energy to be used in many new areas and has the potential to sustainably increase the share of renewable energies in the future.

The new substance is a further development of aerogel discovered by researchers at Stanford in the 1930s 2. According to the definition, an aerogel is an open-cell, mesoporous (material with a pore diameter of less than 50 nm) foam which consists of a network of interconnected nanostructures, that are characterized by a porosity of more than 50%. The classification does not refer to the material, but to the structure in which it is arranged. In general, as in the following text, the focus is on silicon-based aerogel.

Ultimately, aerogel is the dry, pore-rich structure of a silicon-based gel, whereby the liquid components of the gel are removed via a drying process, namely supercritical drying. This creates a material with a density between 0.0011-0.5 g / m 3. On average, aerogels have a density of 0.2 g / m 3 and thus, are 15 times heavier than air. Aerogels hold the following records, among others, due to their unique structure and the properties associated with it. Material with 3:

  • Lowest density – lightest solid (0.0011 g / cm ^ 3 – air: 0.0012 g / cm3)
  • Lowest thermal conductivity – best insulator (0.016 W / m * K)

The material is already actively used as an insulating material, but its possible future areas of application are diverse, as the following research results from MIT illustrate.

Innovation

Researcher Evely Wang and her team at MIT4 started developing a completely transparent aerogel 5 years ago. The aim was to develop an optically transparent, heat-insulating aerogel for solar thermal systems. Due to the lack of transparency of current aerogels, they could not be used sensibly in this area. The integration of an optically transparent aerogel in such a system would allow the sun’s rays to penetrate unhindered, while the generated heat cannot escape, which is one of the main problem of current systems. In February 2020, the researchers reported a breakthrough. They had succeeded in developing an aerogel that was more transparent than glass because it was not reflective.

State-of-the-art: Solar energy systems are able to generate average temperatures between 120-220 ° C. These temperatures can be used to heat rooms, generate steam and operate certain industrial processes. However, such systems have following requirements: expensive optical systems that focus the incident sunlight, special surfaces for the absorption of solar energy, and cost-intensive and maintenance-intensive areas with a vacuum, so that the heat does not escape. Based on these limiting properties, there is only an extremely limited market potential. By using a transparent aerogel, the natural greenhouse effect could be mimicked in an extreme way on a small scale with prosperous results.

In order to test the theory, an aerogel-based solar collector was installed on the roof of MIT, which efficiently lets sunlight through, while preventing heat conduction, convection and thermal radiation at once. Such an aerogel could make costly optical systems, surfaces and areas with vacuum obsolete. During the test phase, data was recorded between 11 a.m. and 1 p.m. on a winter day (1 ° C). It was found that the temperature rose directly and stabilized at over 220 ° C. The researchers succeeded in converting water into steam at 120 ° C.

Potantial

The potential of this material is undeniably huge. Be it the application in the field of energy and heat generation or as an insulation material in window construction. In the US, for example, so much energy is lost through windows every year, that 50 million households could be supplied with electricity by the wasted amount. This equates to about $ 32 billion and is responsible for 350 million tons of CO2 – more than 76 million cars.

Research by MIT5 has shown that one solution to this problem could be to replace the air gap in conventional double-glazed systems with aerogel. The insulation capacity could be increased by 40% and is then 85% of a triple-glazed system, which is rarely installed there due to its high costs. They estimate, that the price of such a system would be half that of triple glazing. In addition, the technology could be quickly integrated into the production process. The aerogel pane is designed in such a way, that it can be easily integrated into the existing double-glazed systems, which are standardized throughout the industry. Thus, they could be produced on existing production lines at low cost and with minimal adjustments.

References
1 https://www.umweltbundesamt.de/daten/energie/energieverbrauch-fuer-fossile-erneuerbare-waerme#textpart-1

2https://www.nasa.gov/vision/earth/technologies/aerogel.html

3https://onlinelibrary.wiley.com/doi/abs/10.1002/adma.201200491

4https://news.mit.edu/2020/making-remarkable-material-even-better-aerogel-0225

5https://news.mit.edu/2020/making-remarkable-material-even-better-aerogel-0225